Odontomas (ODs) are the most frequent odontogenic tumors in Western societies, they are often asymptomatic and discovered during routine radiography The purpose of this report was to describe the case of a 10-year-old child with an odontoma within a dentigerous cyst (DC). The patient presented with a 1-week history of painful swelling involving the right mandible and cheek. An intraoral examination revealed a defect of the oral mucosa behind the permanent mandibular first molar, which resembled an exposed alveolar bone or tooth remnants. Clinical and radiographic evaluation revealed a large erupting OD associated with a dentigerous cyst. The OD was separated into pieces and enucleated together with the dentigerous cyst to preserve the mandible's integrity and because of the patient's age. This is the first report of an erupting OD associated with a DC in a child. Surgical removal might be a challenge when large ODs are encountered.